The first person to sail single-handedly and nonstop around the world has joined others in urging the U.S. Coast Guard to resume a search for four missing British yachtsman who disappeared aboard a 40-foot sailboat in the middle of the Atlantic Ocean last week.

Sir Robin Knox-Johnston, who completed his record-breaking circumnavigation in 1969, has joined the families of the crew in asking the U.S. to restart the search for the crew of the Cheeki Rafiki after the Coast Guard called it off on Sunday saying it believed the possibility of finding survivors was remote.

The boat's charter company said it believed the four men were adrift in a life raft and that the Coast Guard had given up the search too soon, a view shared by Knox-Johnston. An online petition has also been started calling for the resumption of the search, as well as a Facebook page.

"We stow life rafts where they are easily accessible; they have also got hydrostatic release valves on them [and] if the boat sinks they automatically release them and let them float to the surface. Everyone trains for this; every yachtsman goes and does a sea survival course," Knox-Johnston told BBC Radio 5. "This was an experienced crew. They almost certainly would have done that; they would have known the score."

The Cheeki Rafiki's skipper contacted charter company Stormforce Coaching on Thursday, saying the crew was "keeping the situation stable," the firm's principal, Doug Innes, said in a statement.

"Unfortunately we lost contact during the early hours of Friday morning and we believe the crew abandoned to the life raft," Innes said.

"Search and Rescue authorities were mobilised and a mixture of Canadian and US aircraft along with merchant vessels searched throughout Friday and Saturday. Although the search efforts coordinated by Boston were exceptional we are devastated that search has been called off so soon after the abandonment to a life-raft."

On Saturday, a cargo ship, Maersk Kure, reported seeing an upturned hull in the same general vicinity the men were last reported — about halfway between the U.S. East Coast and the Azores Islands.

"Reports from the ship also suggest that there were no signs of life aboard the boat and that the ship did not investigate the upturned hull.

"Petty Officer Rob Simpson, a spokesman for the US Coastguard, was quoted in the Daily Telegraph as saying, 'The Maersk Kure is a 1,000ft container ship which does not have the maneuverability, capacity and ability to help.

" 'It has a fairly limited possibility of picking anything up — it is not designed for search and rescue capabilities or anything like that or trained to do anything like that.' "

Simpson said the Coast Guard had "saturated the area" in a two-day search and that "we would have found them" if it was possible.

The BBC says the Royal Yachting Association named the four crew members as Andrew Bridge, 21, from Farnham, Surrey, the yacht's skipper; Paul Goslin, 56, from West Camel, Somerset; Steve Warren, 52, from Bridgwater, Somerset, and 23-year-old James Male, from Southampton.